Oxide based memory devices can be used in a number of electrical systems and can include two electrodes with a tunnel barrier and an oxygen source between the two electrodes. Oxide based memory devices can operate by applying a positive voltage across the electrodes of the memory device to cause oxygen ions from the oxygen source to move to the tunnel barrier. A negative voltage can be applied across the electrodes of the memory device to cause oxygen ions to move from the tunnel barrier to the oxygen source. The resistivity of the memory device is dependent on the oxygen ion location and changes as the location of the oxygen ions changes, either in the tunnel barrier, in the oxygen source and/or in a portion of each. Therefore, the state of the memory device can change depending on the location of the oxygen ions and the state of the device can be read by applying a read voltage across the electrodes of the memory device.
In oxide based memory devices, the retention of the oxygen ions in the tunnel barrier and/or oxygen source can determine the ability of the memory device to maintain a state. For memory devices that better retain oxygen ions in the tunnel barrier it can also be more difficult to move the oxygen ions to the tunnel barrier, e.g., more current is required. And memory devices that can more easily move oxygen ions to the tunnel barrier, e.g., less current is required, may not satisfactorily retain the oxygen ions in the tunnel barrier. A memory device that exhibits poor retention of the oxygen ions in the tunnel barrier may not be reliable in maintaining an “on” state or an “off” state for the memory device. An oxide based memory device that can move oxygen ions between the oxygen source and the tunnel barrier and retain the oxygen ions in the tunnel barrier may have greater reliability in maintaining an “on” state or an “off” state.